Metallic oxides (ceramics) have been prepared in the past from metallic halides by reacting the metallic halides with water to hydrolize the metallic halide and form a water solution of the metallic halide and an acid. One prior art practice has been to convert the resulting metallic oxyhalide to the desired metallic oxide by heating in a reducing atmosphere for dehalogenation.
One specific process particularly important in the production of enriched uranium dioxide is conventionally carried out by a gas phase diffusion process involving halides of uranium so that it is necessary to convert the uranium halide to oxide. Current practice for converting uranium hexafluoride to uranium dioxide, for example, employs hydrolysis of uranium hexafluoride to give a solution of uranyl fluoride and hydrogen fluoride from which ammonium diuranate is precipitated by addition of ammonia. After filtration, the ammonium diuranate of high fluoride ion content is dissolved in nitric acid with fluoride decontamination of the resulting uranyl nitrate solution being accomplished by solvent extraction. From the resulting purified uranyl nitrate solution, ammonium diuranate is reprecipitated and then calcined to give U.sub.3 O.sub.8 which in turn is reduced with hydrogen to give uranium dioxide with a high fluoride ion concentration, the fluoride ions often being combined with the UO.sub.2 to give uranyl fluoride (UO.sub.2 F.sub.2).
A process of dehalogenation of metallic oxyhalides utilizes heated atmospheres of hydrogen passed over a bed of the metallic oxyhalide. To dehalogenate a metallic oxyhalide such as uranium oxyfluoride one needs, when using hydrogen, a temperature in excess of about 2000.degree. F to have a practical rate of dehalogenation. Such a temperature produces undesirable properties in the resulting ceramic including the loss of the ability to make dense compacted ceramic bodies from the resulting powder due to a deadening of the powder (loss of surface area of the powder) at the temperature required for the dehalogenation process. In order to lower the temperature for conducting successful dehalogenation of metallic oxyhalides a wet hydrogen atmosphere has been used which has the effect of increasing the rate of dehalogenation at any given temperature when compared to the use of dry hydrogen. This also has a practical effect of lowering the temperature needed to achieve a practical rate of dehalogenation of a metallic oxyhalide. The dehalogenation process using wet hydrogen gives economies of operation and an increased powder activity in that there is greater ability of the powder to be compacted and sintered to dense structures.
Improved methods for the conversion of a uranium halide such as uranium hexafluoride to uranium oxide by gas phase reaction of uranium hexafluoride are described in copending U.S. patent application Ser. No. 77,446, now U.S. Pat. No. 3,796,672, entitled "Process for Producing Uranium Dioxide Rich Compositions from Uranium Hexafluoride", filed Oct. 2, 1970 in the names of W. R. DeHollander and A. G. Dada and assigned to the same assignee as the present invention. Briefly this process can be summarized as a method of preparing a uranium dioxide rich composition from uranium hexafluoride in a reactor defining a reaction zone in the presence of an active flame comprising the steps of:
a. introducing a first gaseous reactant comprising a mixture of uranium hexafluoride and an oxygen-containing carrier gas into the reaction zone,
b. separately introducing a second gaseous reactant comprising a reducing gas into the reaction zone, and
c. separately introducing a shielding gas into the reaction zone between the first gaseous reactant and the second gaseous reactant which temporarily prevents substantial mixing and reaction between the first and second gaseous reactants until sufficient cross diffusion of the reactants occurs as the reactants pass through the reaction zone.
Another process is described in copending U.S. patent application Ser. No. 131,685, now U.S. Pat. No. 3,790,493 entitled "Post Oxidation Process for Uranium Dioxide Rich Compositions", filed Apr. 6, 1971 in the names of A. G. Dada, W. R. DeHollander and R. J. Sloat and assigned to the same assignee as the present invention. Briefly this process can be summarized as a method of preparing a uranium oxide rich composition from uranium hexafluoride in a reaction zone in the presence of an active flame comprising the steps of:
a. introducing a first gaseous reactant comprising a mixture of uranium hexafluoride and an oxygen-containing carrier gas into the reaction zone,
b. separately introducing a second gaseous reactant comprising a reducing gas into the reaction zone,
c. separately introducing a shielding gas into the reaction zone between the first and second gaseous reactants which temporarily prevents substantial mixing and reaction between the first and second gaseous reactants until sufficient cross diffusion of the reactants occurs as the reactants pass through the reaction zone, and
d. introducing a third gaseous reactant comprising an oxygen-containing gas into contact with the particulate uranium dioxide rich composition and the residual reducing gas thereby converting the residual reducing gas in the reaction zone to an oxidized form and oxidizing the uranium dioxide rich composition to a higher oxide of uranium.
The powder produced in the practice of the process of U.S. Pat. No. 3,796,672 is largely uranium dioxide or precursors of uranium dioxide with the balance being largely fluoride impurities and including some UF.sub.4, U.sub.3 O.sub.8, U.sub.4 O.sub.9, UO.sub.2 F.sub.2 and mixtures thereof. The powder produced in the practice of the process of U.S. Pat. No. 3,790,493 is largely uranium oxides (U.sub.3 O.sub.8, U.sub.2 O.sub.5, U.sub.4 O.sub.9 and mixtures thereof with or without some UO.sub.2) or precursors of uranium oxides with the balance being largely fluoride ions in the form of hydrogen fluoride and other compounds containing uranium and fluorine believed to include UF.sub.4, UF.sub.6, UO.sub.2 F, UO.sub.2 F.sub.2, and mixtures thereof.
Accordingly it is desirable to use a low temperature process for achieving a practical, rapid rate of dehalogenating compositions such as uranium oxide compositions containing halide impurities including metallic halide impurities such as uranium fluorides and uranium oxyfluorides. The lower temperature dehalogenation process will enable treatment of uranium oxide powders produced by gas phase conversion so that these powders have even greater powder activity, greater economies of operation and more dense structures after the powders are compacted and sintered.